Film casting device and process of making the same



United States Patent Ofifice 2,715,584 Patented Aug. 16, 1955 FILM CASTING DEVICE AND PROCESS OF lVIAKlNG THE SAlVlE William B. Horback, Irvington, and Walter D. Paist,

Berkley Heights, N. J., assignors to Celanese Corporation of America, New York, N. Y., a corporation of Delaware N Drawing. Application May 9, 1952, Serial No. 287,052

16 Claims. (Cl. 1175.1)

This invention relates to film casting surfaces and relates more particularly to a novel process for preparing film casting surfaces and to the film casting surfaces produced by said process.

An important object of this invention is to provide a novel process for the production of film casting surfaces that will produce films free from defects.

A further object of this invention is to provide a novel film casting surface which will be relatively rugged and may be used for extended periods of time.

Other objects of this invention will be apparent from the following detailed description and claims.

According to one process that is widely employed for the production of films, a dope containing a filmforming material is flowed onto the surface of a casting member which may, for example, comprise a rotating, cylindrical casting drum or an endless belt disposed in a horizontal plane and trained over a number of pulleys. After the dope has set, the film is stripped from the casting member and may, if necessary or desirable, be subjected to further treatment. To obtain satisfactory films, the film casting surface on the casting member must be free from defects since any such defects Will be reproduced in the films. To provide a suitable film casting surface on the casting member, it has previously been suggested that the casting member be provided with a coating of a film-forming substitution derivative of cellulose, such as a cellulose ester or ether, and the surface layers of said coating be converted to regenerated cellulose by suitable chemical treatment. Film-casting surfaces prepared in this manner are well suited for the production of blemish-free films and are inexpensive to prepare. However, these film-casting surfaces are relatively soft so that they are prone to scratching or to the development of a matte surface. In addition, they are sensitive to moisture and tend to develop irregularities owing to the absorption of moisture. As a result, the useful life of said film-casting surfaces has been somewhat limited.

It has now been found that film-casting surfaces prepared in the manner described above may be hardened and their sensitivity to moisture substantially reduced by treating said surfaces with a dialdehyde or other suitable material to cross-link the cellulose. Film-casting surfaces which have been treated in this manner exhibit a lesser tendency to scratch or develop a matte surface, and also exhibit a lesser tendency to develop irregularities owing to the absorption of moisture. As a result, the useful life of the said treated film-casting surfaces is appreciably longer than the useful life of untreated surfaces.

Suitable film forming substitution derivative of cellulose materials that may be employed for forming the filmcasting surface of this invention include, for example, the cellulose esters such as cellulose nitrate, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate and cellulose acetate butyrate; and the cellulose ethers such as ethyl cellulose. These substitution derivatives of cellulose materials may be applied to the casting member from solutions in volatile solvents such as, for example, acetone, methylene chloride, acetone/alcohol (:10), nitromethane, dioxane, and benzene/methanol 1:1. The volatile solvent is evaporated leaving behind a coating of the cellulose derivative.

To efiect the regeneration of the cellulose in the surface layers of the coating there may be employedany of a large number of known materials. For example, in the case of cellulose nitrate there may be employed sulfuric acid or ammonium sulfhydrate; in the case of the organic esters of cellulose there may be employed alkaline materials such as sodium or potassium hydroxide; and in the case of the cellulose ethers there may be employed hydrochloric acid and hydriodic acid. These chemical reagents may be applied to the cellulose derivative coating in any desired manner, as, for example, from aqueous or alcoholic solutions. However, a particularly advantageous method of applying these reagents, especially Where the casting member comprises a casting drum, is to incorporate said reagents into a viscous dope containing a film-forming material, casting the said dope onto the cellulose derivative coating to form a film and stripping the said film from the cellulose derivative coating after the regeneration of the cellulose derivative has progressed to the desired extent. This particular method for efiecting the regeneration of the cellulose is more fully described in application S. No. 141,846, filed February 1, 1950, now U. S. Patent No. 2,622,278.

Following the regeneration of the cellulose in the surface layers of the cellulose derivative, the film casting surface is treated so as to cause a cross-linking of the cellulose to take place. Particularly advantageous results have been obtained by applying to the film-casting surface a dialdehyde, such as glyoxal, succinaldehyde (in the form of its inner acetal diethoxy tetrahydrofurane),oc,'y-dimethyl-u methoxymethyl glutaraldehyde and a-hydroxy adipaldehyde and heating the said filmcasting surface until the desired cross-linking of the cellulose has taken place. The dialdehydes may be applied to the film-casting surfaces from aqueous solutions containingbetween about 5 and 30% of the dialdehyde. There is advantageously included with the dialdehyde a small amount, say from about 0.5 to 5% by weight, based on the weight of the dialdehyde, of an acidic material, such as oxalic acid, sulfuric acid, formic acid or p-toluene sulfuric acid to catalyze the cross-linking of the cellulose. Suitable wetting agents may also be employed. Another method for applying the dialdehyde to the film-casting surface is to incorporate the same into a dope containing a film-forming material or thickening agent, hereinafter called a film-forming material, which is substantially inert to the dialdehyde and coating said dope onto the film-casting surface using the standard film-casting hopper. The dialdehyde will diffuse into at least the upper layers of the film-casting surface. The dialdehyde-containing dope may be applied to form one or more layers extending over the entire area of the film-casting surface. After the desired amount of dialdehyde has diffused into the film-casting surface, the dialdehyde-containing layer is stripped off. Alternatively, the dialdehyde-containing dope may be applied to the film-casting surface as a single layer which is stripped from said surface continuously. In this case, the application of the dialdehyde-containing dope is continued for a period long enough to incorporate into the film-casting surface the desired amount of the dialdehyde. Suitable film-forming materials that may be employed to form the dialdehyde containing dope include, for example, cellulose acetate, cellulose propionate,

a sodium carboxy methyl cellulose,

V a cloth 'or the The dialdehydercontaining coating ,of cellulose acetate.

. ethyl cellulose film is stripped from the casting The cellulose acetate coating is converted to regenerated layer While the casting drum is nitrocellulose, sodium cellulose sulfate and ethyl cellulose. Any excess dialdehyde may, if desired, be removed from the outer layer of the film-casting surface by wiping the same with like wettedwith a suitable solvent for the dialdehyde such as acetone. The dialdehyde-containing film-casting surface is then heated to a temperature of between about 50 and 150 C. for a period of between about /2 and 60 hours until the desired crosslinking of the cellulose has taken place. Another method for carrying out the cross-linking of the cellulose is to apply a dialdehyde-containing dope to the film-casting surface and to heat the said surface, while' the dopecoiitaining layer is in place, to the temperatures and for the times specified above or even to lower temperatures of between about 25 and 50 C. for from about 1 to 24 hours to effect fall or a part of the desired cross-linking. dope may then be stripped from the film casting surface and the said surface may then be heated further to expel any residual solvent therefrom and to complete the cross-linking of the cellulose, if necessary.

The cross-linking may also be effected; by any combination of the procedures described above. Film-casting surfaces prepared in this manner have hard, shiny surfaces that are difficult to'scratch or matte, and show a much reduced sensitivity to water as compared with untreated surfaces.

The following examples are given to illustrate this invention further.

Example I The surface of a casting drum is covered with a having. an acetyl value of 56%, calculated as acetic acid. 'Onto this coating there are cast four, superimposed layers of a dope containing 15% by weight of ethyl cellulose, and 0.6% by weight of potassium hydroxide in methanol. After drying, the drum.

cellulose to a depth of 0.0045 inch.

A solution containing 75 parts by weight of glyoxal,

475, parts by weight of water and 2.5 parts by weight of oxalic acid is applied to the surface of the cellulose acetate rotated for revolutions, following which the excess glyoxal is wiped ofi with acetone-wet. cloths and'the casting drum is heated to 75 C. andheld at this temperature for 2.5 hours. The

film-casting surfa'ceis harder and less sensitive to water than the untreated surface.

Example 11 V A casting drum is covered with a cellulose acetate layer having an acetyl value of 44%, calculated as acetic acid, and the surface of said layer is converted to regenerated cellulose in the manner set forth in Example I. There is then coated ontosaid'layer a dope containing 115 parts by weight of 30% by weight aqueous glyoxal, 1.5 parts by weight of oxalic acid and 100 parts by V weight of cellulose acetate, having m acetyl value of 44%,.

4 Example III A' casting drum is covered with a cellulose acetate layer having an acetyl value of 56%, calculated as acetic acid, and the surface of said layer is converted to regenerated cellulose in the manner set forth in Example I. There is then coated onto said layer a dope containing 100 parts by weight of cellulose acetate having an acetyl value of 56%, calculated as acetic'acid, 1 part by weight for l'hour at a temperature of 35 of oxalic acid, 170 parts by weight of 30% by weight aqueous glyoxal and 400 parts by weight of acetone. The glyoxal-containing layer is permitted to remain in place C. during which time the glyoxal diffuses into the regenerated cellulose layer and the cross-linking of the cellulose. begins. a The cellulose acetate film is then stripped from the casting drum and the excess glyoxal on the surface is wipedoff with cloths wet with acetone. The casting drum is then heated to a temperature of 80? C. for a period of 20 hours, during which time the cross-linking is completed and all the volatile solvents are driven off.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departmg from the spirit of our invention. 1

Having described our invention, what'we desire to secure'by Letters Patent is: V

I 1. In a processfor the production of film-casting surfaces, the steps which comprise forming a coating of an organic acid ester of cellulose on a casting member, regenerating the cellulose in the surface layers of said coating, and cross-linking the regenerated cellulose with glyoxal. r r V 2. In a process for the treatment of a film-casting memher having thereon a coating of a film-forming substitution derivative of cellulose, the film-casting surface layers of which have been converted to regenerated vcellulose, the'step which comprises. cross-linking the regenerated cellulose to produce a hard shiny surface having reduced sensitivity to water as compared with an uncross-linked regenerated cellulose.

3. In a process for the treatment of a film-casting memher having thereon a coating of a film-forming substitu- 7 tion derivative ofcellulose, the film-casting surface layers of which have been converted to regenerated cellulose,

-' the step which comprises cross-linking the regenerated cellulose with a dialdehyde."

linked. The cellulose'acetate film is then stripped from V greater than the untreated surface.

4. In a process for the treatment of a film-casting memher having thereon a coating of a film-forming substitution derivative of cellulose, the film-casting surface layers of which have been converted to. regenerated cellulose,

'the step which comprisescross-linking the regenerated cellulose with glyoxal.

r 5. 111a process for the treatment of a film-casting memher having thereon a coating of an organic acid ester of cellulose, the film-casting surface layers of'which have been converted to regenerated cellulose, the step which comprises cross-linking the regenerated cellulose to produce a hard shiny surface having reduced sensitivity to water as compared with an uncross-linked regenerated cellulose.

6. In a process for the treatment of a film-casting memher having thereon a coating of cellulose acetate, the film-casting surface layers to regenerated cellulose, the step which comprises applying glyoxal to the regenerated cellulose layers, and

'cross-linking 'the regenerated cellulose containing the.

the same to a temperature of between C. for a period of between about /2 glyoxal by heating about 50 and 150 and hours. r j

7. In a process for the treatment of a film-casting memher having thereon a coating of a film-forming substitution derivative of cellulose, the film-casting surface lay.-

ers of which have been converted to regenerated cellulose,

the step which comprises cross-linking the regenerated r cellulose by applying to said coating a dope containing of which have been converted.

a film-forming material and a cross-linking agent for the regenerated cellulose comprising a dialdehyde and thereby forming a layer on said coating, the amount of said dialdehyde in said layer being sufiicient to diffuse into said regenerated cellulose coating, and heating the coating until cross-linking of the regenerated cellulose takes place and stripping said layer to expose a surface of the treated regenerated cellulose.

8. A film-casting device comprising in combination, a casting member, and a coating of a film-forming substitution derivative of a cellulose on said casting member, said coating having on its upper surface a layer of crosslinked regenerated cellulose, the exposed film-casting surface of said cross-linked regenerated cellulose being hard and shiny and of reduced sensitivity to water as compared With an uncross-linked regenerated cellulose.

9. A film-casting surface comprising in combination, a casting member, and a coating of a film-forming substitution derivative of cellulose on said casting member, said coating having on its upper surface a layer of regenerated cellulose cross-linked with a dialdehyde.

10. A film-casting surface comprising in combination, a casting member, and a coating of a film-forming substitution derivative of cellulose on such casting member, said coating having on its upper surface a layer of regenerated cellulose cross-linked With glyoxal.

11. A film-casting device comprising in combination, a casting member, and a coating of a cellulose ester on said casting member, said coating having on its upper surface a layer of cross-linked regenerated cellulose, the exposed film-casting surface of said cross-linked regenerated cellulose being hard and shiny and of reduced sensitivity to Water as compared with an uncross-linked regenerated cellulose.

12. A film-casting surface comprising in combination, a casting member, and a coating of an organic acid ester of cellulose on said casting member, said coating having on its upper surface a layer of regenerated cellulose crosslinked with a dialdehyde.

13. A film-casting surface comprising in combination, a casting member, and a coating of cellulose acetate on said casting member, said coating having on its upper surface a layer of regenerated cellulose cross-linked with glyoxal.

14. A film-casting surface comprising in combination, a casting member, and a coating of cellulose acetate on said casting member, said coating having on its upper surface a layer of regenerated cellulose cross-linked with succinaldehyde.

15. A film-casting surface comprising in combination, a casting member, and a coating of cellulose acetate on said casting member, said coating having on its upper surface a layer of regenerated cellulose cross-linked With a,'y-dimethyl-cc-methoxymethyl glutaraldehyde.

16. A film-casting surface comprising in combination, a casting member, and a coating of cellulose acetate on said casting member, said coating having on its upper surface a layer of regenerated cellulose cross-linked with a-hYdIOXY adipaldehyde.

References Cited in the file of this patent UNITED STATES PATENTS Francis et a1. July 18, 1944 Pfeifer et al. Feb. 17, 1948 OTHER REFERENCES 

2. IN A PROCESS FOR THE TREATMENT OF A FILM-CASTING MEMBER HAVING THEREON A COATING OF A FILM-FORMING SUBSITUTION DERIVATIVE OF CELLULOSE, THE FILM-CASTING SURFACE LAYERS OF WHICH HAVE BEEN CONVERTED TO REGENERATED CELLULOSE, THE STEP WHICH COMPRISES CROSS-LINKING THE REGENERATED CELLULOSE TO PRODUCE A HARD SHINY SURFACE HAVING REDUCED SENSITIVITY TO WATER AS COMPARED WITH AN UNCROSS-LINKED REGENERATED CELLULOSE. 